The Social Explorer produces maps and reports of US Census Tract level data from 1940-2000. Using high quality maps and data, they make available the full contents of the tract data for the United States for the full period. The data can also be exported as excel spreadsheets for easy reuse.

Historical Census Browser
Population and housing data for all U.S. states and counties, 1790 to 1960, based on decennial census of population and housing. Provides basic counts of population and housing, including race, gender, and some measure of household size and composition. For 1840 to 1960, economic characteristics such as education and occupation are included. Later decades have many variables, including ancestry, literacy, and income variables.

Decennials - Census of Population and Housing
PDF-format versions of historic US decennial census volumes, 1790 to present. Topics covered include basic counts of population and housing, with race and gender, for the nation, states, counties, townships and municipalities, and some small areas (e.g., wards). From 1840 to present, social and economic information is provided.
Holdings: 1790 to present (backfile in progress: 1790-1860, 1990-2000 available)